Pump or motor



PUMP 0R MOTOR Filed Feb. 18, 1955 5 Sheets-Sheet 2 TEIHNEY.

Feb. 2, 1937. w. FERRIS PUMP 0R MOTOR Filed Feb. 18, 1935 3 Sheets-Sheet 3 VVALTEF! FEF'R'IS I 7BY I y A r'rnFeNEY.

Patented Feb. 2, 1937 UNITED STATES PAT NT orrlca Oilgear Compa Milwaukee,

ration of Wisconsin Wis a corpo- Application February is, 1935, Serial No. 6,967 '19 Claims. '(Cl. 103-162) in as a pump and the invention will beexplained as applied to a pump, but it is to be understood that .the invention is equally applicable to a motor of the same type. a The pump to which the invention applies in particular is provided with a thrust member 7 which engages the outer end or head of each piston' upon a single spot offset from the piston axis '20 whereby the outer end or head of each piston will roll along the thrust member and each piston will rotate in its cylinder as it reciprocates therein, such as the pump described and claimed in Patent No. 1,998,984, issued April 23, 1935 on my copending application, Serial No. 699,847 filed November 27, 1933 and in application, Serial No.

662,219 filed March 23, 1933 of which this application is a continuation as to matters common to .both applications. 30. The present invention has as an object to provide a rolling piston pump of the axial type.

Another object is to provide an axial type of pump which is capable ofdeveloping high pres-- sures. Another object is to provide an axial type of pump which is highly eflicient.

Other objects and advantages will appear from g 1 the following description of the pump illustrated.

in the accompanying drawings in which the views are as follows:

Fig. 1 is a central longitudinal section through a pump in which the, invention is embodied.

Fig. 2 is a fragmentary longitudinal section taken at right angles to the plane of Fig. 1, as indicated by the line 2-2 'of Fig. 3.

Fig. 3 is a transverse vertical section taken on the line 3-3 of Fig. 1.

Fig. 4 is a transverse vertical section taken on the line 4-4! of Fig. 1.

i Fig. 5 is a transverse vertical section taken on the line 5--5 of Fig. 1.

The pump chosen for illustration is provided with a'casing I having feet or bases 2 fixedthereto for supporting the same.

: I The'casing is closed at its front end by rernovable front plate or head 3 and at its rear-end by an end wall or head which is shown as being integral with the side walls of the casing and provided with aboss 4. j I, The casing has a cylinder barrel '5 arranged 5 therein and adapted to be rotated by a drive shaft 6 with which it is fixed for rotation as by being splined thereon. The shaft 6 extends through the front plate 3 fdnconnection to a prime mover and is jour aled in antifriction 1 bearings I and 8 carried, respectively, by the front plate 3 and the boss 4. Leakage of liquid through the front plate 3 is prevented by a packing or gland 9 arranged upon the shaft 6 and retained in position outward of the bearing 1 by a 15 can It fastened to the front plate 3,

The cylinder barrel. 5 has formed therein a plurality of cylinders H which are arranged parallel to the axis thereof, and equally spaced around. the shaft 6, nine cylinders-being shown.

' axis parallel to the cylinder barrel axis. The reaction surface ll engages each piston head upon a single spot which remains upon the outside of the piston axis in respect to thecylinder barrel 35 'axis throughout a complete revolution of the cylinder barrel.

However, the thrust member l5 may be pro-- vided with an external conical reaction surface which engages each piston head at a point in- 40 side the piston axis. This construction has not been illustrated as it is simply the reverse-of the l construction shown. Also, under certain conshaping the outer end or head into the form of a truncated cone and then generating the contact surface by holding it in contact "with a grinding surface corresponding to the reaction surface It, 55

gages the under sides of all of the piston heads,

l3 and is mounted upon a collar 22 which is. fitted upon the shaft I to slide thereon. The .inner surface of the wabbler plate 22 and the outer surface of the collar 22 are spherical and complementary to each other to permit the plate 22 to tilt on the collar 22 as the cylinder barrel rotates. The plate 22 and the collar 23 are urged tion, the ro'tative speed of the cylinder barrel would be limited by the rotative speed which could be imparted to the pistons, thereby limiting the volumetric delivery of the pump. For this reason,

the thrust member I! is rotatably supported as by means of an antifriction bearing IS the axis of which coincides with the axis of the conical reaction surface I.

The bearing I8 is carried by a reaction member or support I! which is restrained from axial or rotative movement but which, in a variable displacement pump, is adjustable transversely of the cylinder barrel axis to change the stroke of the pistons. i

As best shown in Fig. 2, the support i1 is restrained from movement away from the cylinder barrel 5 by two abutments [8 which are'can'ied by the front plate 3 upon opposite sides-of the shaft 8 and engage the front face of the support l1 near each of its lateral sides.

' As best shown in Figs. 2 and 3, the support I! is restrained from lateral movement by two guides l9 which are fixed upon the front face thereof with the outer edge of each guide in contact with the inner edge of an abutment i8.

- The abutments l8 and the guides I 9 prevent the support I! from moving in two directions but permit it to be moved vertically either by hydraulic or mechanical means both of which are in common use. As shown in Fig. 1, a screw 20 is threaded through the top of the casing l and attached to the support I! by a connection which permits it 'to rotate independent thereof.

The screw 20 is provided upon its upper end with a hand wheel 2| by means of which it may be rotated to raise or lower the support l1 and the thrust member 15 to thereby vary the stroke of the pump.

When the axis of the reaction surface I4 coincides with the cylinder barrel axis, the point of contact between each piston head and the reaction surface remains at the same distance from other half-revolution, thereby forcing each piston rearward into its cylinder to expel liquid therefrom during one half-revolution and permitting each piston to move forward and liquid to enter its cylinder during the other half-revolution.

The piston may be moved forward or outward and the head thereof retained in contact with the reaction surface It in any suitable manner, such as by supplying the cylinders on the intake side forward to hold the piston heads I! in contact with the reaction surface H by a helical compression spring 24- which encircles the shaft 6, engages the rear face of the collar 23, and reacts against the cylinder barrel.

As the cylinder barrel. rotates and the thrust member forces the pistons on the discharge side of the pump inward to expel liquid from their cylinders, the wabbler plate 22 will tilt upon the collar 23 and move the pistons on the intake side of the pump outward and enable them to draw liquid into their cylinders.

Liquid flows to and from each cylinder through apassage 25 which is formed in the cylinder barrel and has its inner end in communication with the cylinder and its outer end functioning as a port to communicate with opposite sides of an external hydraulic circuit alternately as the cylinder barrel rotates.

Liquid may flow to and from the cylinders through a central valve shaft or pintle as shown in my copending applications referred to above, in which case the port ends of the passages 25 will open into the bore of the cylinder barrel and communicate alternately with two ports formed in the pintle.

However,-the passages 25 are shown as terminating upon the rear end of the cylinder barrel which bears against a flat yalve plate 26 having in the boss I for connecting the pump to an external circuit as by means of pipes 32 and II fastened to the boss 4 in communication, respectively, with the passages 30 and II.

If the thrust member l5 israised above its central or neutral position, as shown in Fig. 1, and the cylinder barrel I is rotated in the direction of the arrow shown in Fig. 4,-the pistons in the lower half of the cylinder barrel will be progressively urged inward by the reaction surface l4 and expel liquid from their cylinders through the passages 25, the port 22, and the passage 2| into the pipe 22, and the pistons in the upper half of the cylinder barrel will be progressively drawn outward by the wabbler plate 22 and draw liquid into their cylinders from the pipe 22 through the passage 20, the

port 21 and the passages 25.

If the thrust member ismoved downward .until its axis is below, the axis of the cylinder barrel, the pump will deliver liquid into the pipe 22 and draw liquid into its cylinder from the pipe 88. In each instance, the rate at which the pump delivers liquid will depend upon the distance the axis of the reaction surface 'llfi's 'oifset from the cylinder barrel axis. Also, rotation of the cylinder barrel in the opposite direction will cause the pump to deliver liquid in the opposite direc-v tion.

As previously pointed out, the thrust member i5 engages each piston upon a single spot which is offset from the piston axis. Consequently. all pumping forces are transmitted from the thrust member to the piston at an angle to the piston, axis. This spot is so positioned that the line of force, indicated by the line 34 in Fig. 1, passes through the valve plate 26 and preferably passes through the valve plate port, in order that the pumping forces may not tend to tilt the cylinder barrel and thereby cause excessive leakage from between theend of the cylinder barrel and the face of the valve plate.

, A film of liquid is maintained between the end of the cylinder barrel and the face of the valve plate, and pressure created by the'pump extends into this film and tends to separate the cylinder barrel from the valve plate. In order to overcome this tendency, the port end of each passage 25 is made smaller than the cylinder ii and the contact width between cylinder barrel 5 and valve plate 26 is made narrow so that the'pumping forces may hold the cylinder barrel firmly in engagement with the valve plate.

rel rotates, a cylindrical piston fitted in each cylinder and having a contact surface arranged upon its outer end at an angle to'its axis and fixed for rotation with its inner part, and a rotatable thrust member restrained from movement along the axis of said cylinder barrel and provided with an internal substantially conical reaction surface engaging the contact surface on each piston upon a single spot which remains upon the same side of the piston axis in respect,

to the cylinder barrel axis throughout a complete revolution of said cylinder barrel, said thrust member causing said pistons to reciprocate and ,rotate in said cylinders and said contact surfaces to roll along said reaction surface during rotation of said cylinder barrel.

2. A pump, comprising a stationary valve member having intake and exhaust ports, a rotatable cylinder barrel having cylinders arranged therein parallel to its axis of rotation and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder'barrel rotates, a piston fitted in each cylinder and having a contact surface arranged upon its outer end at an angle to its axis, a

thrust member restrained from movement along the axis of said cylinder barrel and having its axis offset from the axis of said cylinder barrel cylinder barrel axis throughout a complete revolution of said cylinder barrel and which is offset far enough from the piston axis to cause the contact surface on that piston to roll along said reaction surface during rotation of said cylinder barrel, and means for adjusting said pump to vary the distance between the axis of said cylinder barrel and the axis of said thrust member to thereby vary the stroke of said pistons.

3. A pump, comprising a stationary valve member having intake and exhaust ports, a. ro-

tatable cylinder barrel having cylinders arranged therein parallel to its axis of rotation and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted in each cylinder and having a contact'surface arranged. upon its Ioute'r end at an angle to its:

axis and fixed for rotation with its inner part; a thrust member restrained from movement along the axis of said cylinder barrel and having its axis offset from the axis of-said cylinder barrel when the pump is delivering liquid, said thrust member being provided with a reaction surface inclined to the axis of each piston in the same direction in respect to the axis of said cylinder barrel and engaging the contact surface on each piston upon a single spot which remains upon the same side of the piston axis in respect to the cylinder barrel axis throughout a complete revolution of said cylinder barrel and which is barrel and the axis of said thrust member to thereby vary the stroke of said pistons. I

4. A pump, comprising a stationary valve member having intake and exhaust ports, a rotatable cylinder barrel having cylinders arranged therein parallel to its axis of rotation-and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a piston fitted in each. cylinder and having a contact surface arranged upon. its outer end at an angle to its axis, a thrust member restrained from movement along the axis of said cylinder barrel and having its axis offset from the axis of said cylinder barrel when the pump is delivering liquid, said thrust member being provided with a reaction surface inclined to the axis of each piston in the same. direction in respect to the axis of said cylinder barrel and engaging the contact surface on each piston upon a single spot which remains upon the same side of the piston axis in respect to the cylinder barrel axis throughout a complete revolution of said cylinder barrel and which is offset far enough from the piston axis to cause the contact surface on that piston to roll along said. reaction .sur-

. face during rotation of said cylinder barrel, and

means for rotatably supporting said thrust 'member to permit it to rotatein unison with said 5. 'A pump, comprising a stationary valve me m ber having intake and'exhaust ports; a rotatable cylinder barrel having cylinders arranged therein parallel to its axis of rotation and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a piston fitted in each cylinder and havinga contact surface arranged upon its outer end at an angle, to its axis, a thrust member recylinder barrel. I

strained from movement along the axis of said 7 cylinderbarrel and having its axis offset'from the axis of said cylinder barrel when the pump is delivering liquid, said thrust member being provided with a reaction surface inclined to the axis of each piston in the same'direction in respect, to the axis of said cylinder barrel and en.- gaging the contact surface on each pistonupon a single spot which remains upon the same side of the piston axis in respect to the cylinder barrel axis throughout a complete revolution of said cylinder barrel and which is offset far enough from the piston axis to cause the contact surface on that piston to roll along said reaction surface during rotation of said cylinder barrel, means for rotatably supporting said thrust member to permit it to rotate in unison with said cylinder barrel, and means for adjusting said pump to vary the distance between the axis of said thrust member and the axis of said cylinder barrel to thereby vary the stroke of said pistons.

6. A pump, comprising a stationary valve plate having intake and exhaust ports, a cylinder barrel rotatable upon a stationary axis in contact with said valve plate and having cylinders arranged therein parallel to its axis and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted in each cylinder and having a contact surface arranged upon its outer end at an angle to its axis and fixed for rotation with its inner part, and a rotatable thrust member restrained from movement along'theaxis of said cylinder barrel and provided with an internal substantially conical reaction surface engaging the contact surface on each piston upon a single spot which remains upon the same side I of the piston axis in respect to thecylinder barrel axis throughout a complete revolution of said cylinder barrel, said thrust member causing said pistons to reciprocate ,and rotate in said cylinders and said contact surfaces to roll along said reaction surface during rotation of said cylinder barrel.

7. A pump, comprising a stationary valve plate having intake and exhaust ports, a cylinder barrel rotatable upon a'stationary axis in contact with said valve plate and having cylinders arranged therein parallel to its axis and provided With ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted in each cylinder and having a contact surface arranged upon its outer end at an angle to its axis and fixed for rotation with its inner part, a thrust-member restrained from movement along the axis of said cylinder barrel and having its axis offset from the .axis of said cylinder barrel when the pump is delivering liquid, saidthrust member being provided with a reaction surface inclined to the axis of each piston in the same direction in respect to the axis ofsaid cylinder barrel and engaging the contact surface on each piston upon .a single spot which remains upon the same side of the rel rotatable upon a stationary axis in contact with said valve plate and having cylinders arranged therein parallel to'its axis and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted-in each cylinder and having a contact surface arranged upon its outer end at an angle to its axis. and fixed for rotation with its inner part, a thrust member restrained from movement along the axis of said cylinder barrel and having its axis offset from the axis of said cylinder barrel when the pump is delivering liquid, said thrust member being provided with a reaction surface inclined to the axis of each pistonin the same direction in respect.to the axis of said cylinder barrel and engaging the contact surface on each piston upon ing rotation of ,said cylinder barrel, means for rotatably supporting said thrust member to permit it to rotate in unison with said cylinder barrel, and means for moving said supporting means and said thrust member transverse to the axis of said cylinder barrel to thereby vary the stroke 'of said pistons. I

9. A pump, comprising a stationary valve plate having intake and exhaust ports, a cylinder barrel rotatable upon a stationary axis in contact with said valve plate and having cylinders arranged therein parallel to its axis and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted in each cylinder, an enlarged head fixed upon the outer arranged upon its outer face at an angle to its axis, and a rotatable thrust member restrained from movement along the axis of said cylinder barrel and provided with a substantially conical reaction surface and engaging the contact surface on each piston head upon a single spot which isofiset far enough from the piston axis to cause said piston head to roll along said reaction surface during rotation of said cylinder barrel, the contact spot on the head of each piston being so positioned in' respect to the piston axis that end of each piston and having a contact surface the line of the pumping force transmitted through that spot passes through said valve plate at a point near enough to said exhaust'port to prevent said cylinder barrel from tilting in respect to said valve plate.

10. In a pump, thecombination of a stationary valve member having intake and exhaust ports, a cylinder barrel rotatable in contact with said .valve member and having cylinders arranged therein parallel to its axis of rotationand provided with ports to communicate with said in take and exhaust ports alternately as said cylinder barrel rotates, a cylindrical'piston fitted in each cylinder and provided at its outer end with a head'fixed for rotation'with' its inner end,

a thrust member restrained from movement along the axis of said cylinder barrel and having its axis arranged parallel to and offset from the 2,069,651 cylinder barrel axis when the pump is delivering liquid, a reaction surface arranged upon said thrust member and inclined to the axis'of each piston'in the same direction in respect to'the axis of said cylinder barrel, said reaction surface engaging eachpiston head upon a single spot which is offset far enough from the piston axis to cause the piston head to roll along said reaction surface during-rotation of said cylinder barrel,

valve memberhaving intake and exhaust ports,

a cylinder barrel rotatable in contact with said valve member and having cylinders arranged therein parallel to its axis of rotation and-provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted in each cylinder and provided at its outer end with a head fixed for rotation with its inner end, a thrust member restrained from movement along the axis of said cylinder barrel and having its axis arranged parallel to and offset from the cylinder barrel axis when the pump is delivering liquid, a reaction surface arranged upon said thrust member and inclined to the axis of each piston in the same direction in respect to the axis of said cylinder barrel, said reaction surface engaging each piston head upon a single spot which is offset far enough from the piston axis to cause the piston head to roll along said reac- 7 tion surface during rotation of said cylinder barrel, an arcuate contact surface generated upon each piston head and of a form corresponding tothe surface produced by said head rolling upon said inclined reaction surface, and means for rotatably supporting said thrust member to permit it to rotate in unison with said cylinder barrel. I 12. In a pump, the combination of a stationary valve member having intake and exhaust ports, a

cylinder barrel rotatable in contact with said valve member and having cylinders arranged therein parallel to its axis of rotation and pro-v vided with ports to communicate with said intake and exhaust ports alternately as said cylinderbarrel rotates, a cylindrical piston fitted in each cylinder and provided at its outer end with a head fixed for rotation with its inner end, a thrust member restrained from movement along the axis of said cylinder barrel and having its axis arranged parallel to and offset from the cylinder barrel axis when the pump is delivering liquid, a

reaction surface arranged upon said thrust member and inclined to the axis of each piston in the same direction in respect to the axis of said cylinder barrel, said reaction surface engaging each piston'head upon a single spot which is offset far enough from the piston axis to cause the piston head to roll along said reaction surface during rotation of said cylinder barrel, an arcuate contact surface generated upon each piston head and of a form corresponding to the surface I produced by said head rolling upon said inclined reaction surface, means for rotatably supporting said thrust member to permit it to rotate in unison with said cylinder barrel, and means for adjusting said pump to vary the distance between -the.axis of said thrust member-and the axis of said cylinder barrel to thereby vary the stroke of said pistons. 13. In a pump, the combination of a stationary valve member having intake and exhaust ports, a

cylinder barrel rotatable in contactwith said. 7

valve member and having cylinders arranged therein parallel to its axis of rotation and provided with portsto communicate with said intake and exhaust ports alternately assaid cylin- 'der barrel rotates, a cylindrical piston fitted in each cylinder and provided at its outer end with an enlarged head fixed for rotation with its inner,

end, a thrust member restrained from movement I along the axis-of said cylinder barrel and having cause the piston head to roll along said reactionsurface during rotation of said cylinder barrel, and an arcuate) contact surface generated upon 'each piston head and of a form corresponding to the surface produced by said head rolling upon said inclined reaction surface, means for rotatably supporting said thrust member to permit it to rotate in unison with said cylinder barrel and means engaging the undersides .of said piston heads for retaining said contact surfaces in contact with said reaction surface.

14.- In a pump, the combination of a stationary valve member having intake, and exhaust ports, a cylinder barrel rotatable in contact with said valve member and having cylinders arranged therein parallel to its axis of rotation and provided with ports to communicate with said intake i andexhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted in each cylinder and provided at its outerend with an enlarged head fixed for rotation with its inner end, a thrust member restrained from movement. I along the axis of said cylinder barrel and having its axis arranged parallel to and-offset from the cylinder barrel axis when the pump is delivering liquid, a reaction surface arranged uponv {said face during rotation of said cylinder barrel, an

'arcuate contact surface generated upon each piston head and of a form corresponding to the surface produced by said head rolling upon said inclined reaction surface, means for rotatably supporting said thrust member to permit it to rotate in unison with said cylinder barrel, means for adjusting said pump to vary the distance between the axis of said thrust member and the axis of said cylinder barrel to thereby vary the stroke of said pistons, and means engaging the undersides of said piston heads for retaining said contact surfaces'in contact with said reaction surface. 1

15.; A pump, comprising a stationary flat valve plate having intake and exhaust ports, a cylinder barrel rotatable in contact with said valve member and having cylinders arranged therein parallel toits axis of rotation and pro-' vided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrelv rotates, a cylindrical piston fitted in each cylinder and provided at its outer end with a head fixed for rotation with its inner end, a 75 set far enough from the piston axis to cause the piston head to roll along said reaction surface lofduring' rotation of said cylinder barreL'and an 6 thrust member restrained'from movement along "the axis of said cylinder barrel and having its axis arranged parallelto and offset from the cylinder barrel axis when the pump is delivering liquid, a substantially conical reaction surface arranged upon said thrust member and engaging each piston head upon a single spot'which is 0!- arcuate contact surface generated upon each piston head and of a form corresponding to the surface produced by said head rolling upon said conical reaction surface.

18. A pump, comprising a stationary fiat valve Y plate having intake and exhaust ports, a cylinder barrel rotatable in contact withsaid valve member and having cylinders arranged therein parallel to its axis of rotation and provided with ports cylinder barrel and having its axis arranged parallel to and offset from the cylinder barrel axis when the pump is delivering liquid, a substantially conical reaction surface arranged 1190! said thrust member and engaging. each piston head upon a single spot which is ofiset far enough from the piston axis to r cause the piston head to roll along said reaction surface duringrotation of said cylinder barrel, an arcuate contact surface generated upon each piston headand of a form corresponding to the surface produced'by'said head plate havingintake and'exhaust: ports, a cylinder barrel rotatable in contact wtih said valve member and having cylinders arrangedtherein par-- allel to its. axis of rotation and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted in each cylinder and provided at its outer end with a head fixed for rotation with its inner end, a thrust member restrained from movement along the axis of said cylinder barrel and having its axis arranged parallel to and oflset from the cylinder barrel axis when the pump is delivering liquid, a substantially conical reaction surface arranged upon said thrust member and enga ing each pis ton head upon a single spot which is offset far enough from the piston axis to cause the piston head to roll along said reaction surface during rotation of said cylinder barrel, an/arcuate contact surface generated upon each piston head and of a form corresponding to the surface produced by said head rolling upon said conical reaction surface, .means for rotatably supporting said thrust member to permit it to rotate in unison with said cylinder barrel, and means for movmam ing said supporting said'thruit member transverse to the axis of said cylinder to thereby vary thestroke-of said pistons-I I.

1s. a pump. comprising a stationary fiat valve plate having intake and exhaust ports, a cylinder barrel rotatable in said'valve'memberand having cylinders" 'tbereinwparallel to its axis'of rotation'and ports to communicate with said-,intake'snd exhaust portsv alternately as saidrotates, a cylindrical piston fitted in and provided at its outer end with an enlarged" head fixed-for rotation with its-inner end,-- a

- thrust member restrained from the axis of said cylinder barrel and having its axis arranged parallel to and offset from the cylinder 1 barrel axis when the pump is delivering liquid.

a substantially conical reaction surface arranged upon said thrust member and e each piston head upon a single spot which 'is 'ofi'st -far enough fromvthe piston axis to cause the piston headto roll along said reaction surface during rotation of said cylinder barrel. an arcuate con tact surface generated upon each piston head. and of a form corresponding to the surface produced by said head rolling upon said reaction der barrel rotatable in contact with said valve I a member and having cylinders arranged therein parallel to its axis of rotation and provided with ports to communicate with said intake and exhaust ports alternately as said cylinder barrel rotates, a cylindrical piston fitted .in each ,cylin;

larged head fixed for rotation with its inner end,

means for rotatably supporting said thrust member to. permit itto rotate inunison V40 der and provided at its outer end with 'an ena thrust member restrained from movement along the axis of said cylinder barrel and its axis arranged parallel toand offset'from the cylinder barrel axis whenthe pump is delivering liquid, a substantially conical reaction surface arranged upon said thrust member and engaging each piston head upon a single spotwhich is offset far enough from the nistonaxis-to cause the piston head to roll alongsaid reaction surface .during rotation of said cylinder barrel, and an arcuate contact surface generated upon each piston head and of a form corresponding to the surface produced by said head rolling upon said conical reaction surface, means for rotatably-sup ton heads for retaining said piston heads for retaining said contact surfaces in contact with said reaction surface.

WALTER F'ERRIS. 

